In association with miniaturization of information equipment, electronic components to be installed in the information equipment also have rapidly developed to be reduced in thickness thereof in recent years. In order to cope with narrowing of the connection terminal and reduction of the mounting area by any requirement of the thickness reduction, a ball grid array (hereinafter, referred to as “BGA”) in which electrodes are provided on a back surface thereof has been applied to the electronic component (see, for example, Patent Document 1).
As the electronic component to which the BGA is applied is, for example, a semiconductor package is exemplified. In the semiconductor package, a semiconductor chip having electrodes is sealed with resin. On the electrodes of the semiconductor package, solder bumps are formed. Each solder bump is formed by joining a solder ball to the electrode of the semiconductor package.
In the semiconductor package to which the BGA is applied, the solder bumps are mounted on the electrodes of the substrate to which solder paste has been applied with the solder bumps being aligned and by joining the solder bumps to the electrodes through thermally melted solder paste, the semiconductor package is installed onto the substrate.
Meanwhile, a flux component contained in the solder paste contains a component that is not decomposed or evaporated by heating during soldering, and therefore, such component remains around a soldered portion as a flux residue after the soldering.
In the semiconductor package or the like to which the BGA is applied, there is a case where the flux residue needs to be removed by washing. For this reason, water-soluble flux that can be removed by washing has been proposed (see, for example, Patent Document 2).